Enhancing The Anti-wettibility By Porechannel Modification In Membrane Distillation

Membrane distillation has potential applications in wastewater treatment,desalination and fruit juice condensation.However,it is still in its early stage of industrial development.One of major obstacles in application is membrane wetting.In this paper,a new method of pore channel modification was investigated,andcompositemembranes with anti-wetting properties were fabricated by modifing polyvinylidene fluoride?PVDF?with graphene oxide?GO?.SiO₂-PVDF composite membrane was also prepared by dynamical formationfor comparison purpose.The effects of modification on surface morphology and chemistry were characterized by variety of techniques such as SEM,TEM,AFM,FTIR.The pore size and pore size distribution,gas permeability,Zeta potential and hydrophobicity of the membranes before and after modification were compared.The anti-wettibility of the pristineand modified membranes in simulated seawater with anionic,cationic and non-ionic surfactants was examined in direct-contact membrane distillation?DCMD?.GO was mainly located on the pore surface of membrane bulk,rather than being formed as an individual layer on the membrane surface like SiO₂.Comparingwith the pristine PVDF membrane,the anti-wetting behavior and distillate flux of the GO-modified membranes were improved,especially when anionic surfactant as the foulant,thedistillateconductivity was below 42?S/cm.The enhanced anti-fouling property can be attributed to the oxygen containing functional groups of GO and the healing of membrane pore defects.In order to improve the anti-wettability of GO-PVDF membrane,thecomposite membrane was furthermodified by perfluorooctyl three chlorosilane?PFTS?.The effects of GO/PFTSratioon hydrophobicity were investigated.Microstructure and elemental analysis proved that PFTS not only adhered to membrane surface,but also to porechannels.When anionic,cationic and non-ionic surfactantswere used as the foulantsin the DCMD process,the distillateconductivity of PFTS-GO-PVDF compositemembraneswerebelow23,37and147?S/cmduring25hoperation,respectively,which showed perfectanti-wettability.